PARAMETRIZATION OF ABSORPTION-LINE PROFILES

The parametrization (E)=C+K[(12K)BK+(E-EK)AK][(E-EK)2+(12K)2] for attenuation cross sections (particularly photo-ionization) is discussed, with attention to the following details: prescriptions for exact calculation of profile parameters, in which the effects of distortions are separated from the effects of multiple scatterings; the validity of assuming independent (noninterfering) resonances; the specific case of autoionizing lines; connections with alternative parametrizations; the prohibition on negative cross sections assured by unitarity; behavior at threshold; and the applicability of this parametrization to emission lines. © 1968 The American Physical Society.